1. Field of the Invention
This invention relates to a semiconductor memory device and a method of fabricating the same, and more particularly to a semiconductor memory device such as a DRAM having a large capacity capacitor formed, in a small space, and a method of fabricating such a capacitor easily.
2. Description of the Related Art
For a dynamic memory (DRAM), a storage capacitor and a cell transistor are indispensable, and to move highly integrate the memory, it is necessary to reduce the area of storage capacitor. However, the prevention of soft errors caused by alpha-particle or noise, advantageously results when the capacity of the storage capacitor is larger. To solve this contradiction, it has been attempted to etch grooves in the silicon substrate and use the sidewall of the grooves as storage capacitor. One of the examples of this structure was proposed as "Structure sharing the isolation layer and storage capacitor in a dynamic RAM" at lecture numbers 9.3, 9.4, 9.5 at the International Electron Device Meeting (IEDM) held in the United States in December 1984. This proposal is unique in that the storage capacitor and the isolation layer are fabricated in one common groove. That is, by forming the storage capacitor on the sidewall of a groove, its area is increased. The devices are isolated by the bottom of the groove.
In the conventional memory cell structure in this example, the storage capacitor is formed at the side of a cell transistor, at a position isolated from this transistor. Accordingly, to directly and more highly integrate this memory cell structure, it is necessary to etch the groove deeper, which may give rise to difficulty in the fabricating process. Besides, because of its specific structure, the process may be extremely complicated.